The present invention relates to a container used for the storage or discharge of a high purity liquid chemical, which is employed in the fields of semiconductors and liquid crystals.
The rule for designing, for instance, integrated circuits have increasingly required a high degree of miniaturization thereof because of the recent rapid progress in the electronic devices. High purity liquid chemicals such as liquid photoresists used for such fine patterning techniques should not give rise to any quality deterioration, during the storage and transportation thereof, such as an increase in the amount of impure fine particles in such a liquid chemical, degeneration of components thereof, quantitative changes in the composition, an increase in the quantity of impure metal elements present therein or deterioration of light-sensitive components due to irradiation of the chemical with light rays. The increase in the quantity of impure fine particles in such a liquid photoresist and the degeneration of the components thereof are mainly caused by dissolution of some components present in the container material into the liquid photoresist. If a photoresist film is formed by applying such a contaminated liquid photoresist onto the surface of a substrate, pinholes would be formed thereon. In addition, the quantitative changes in the composition of the liquid are resulted from the permeation of an organic solvent present in the liquid into the exterior through the wall of the container. The liquid accordingly entrains a change in its viscosity and the thickness of the resulting photoresist film is correspondingly changed. The quality deterioration of these liquid photoresists has serious adverse effects on the quality of the resulting semiconductors and liquid crystal displays and yields thereof and would, in turn, shorten the lifetime of the liquid per se.
It has been known that the term "cleanness" is used as an indication for estimating the extent of the quality deterioration of a liquid photoresist in container due to any release of impure fine particles from the container into the liquid during the storage thereof over a long period of time. The cleanness is evaluated by storing ultra high pure water or a liquid photoresist in a container to be tested for a predetermined period of time and then determining the number of fine particles, whose particle size is not less than 0.2 .mu.m, included in 1 ml of the liquid stored in the container. More specifically, the cleanness can be defined by the following equation: EQU Cleanness (particles/ml)=[c(particles).times.a/2(ml)]/[b(ml).times.a(ml)] (1)
In the equation (1), a represents the volume of the container, and b represents the quantity of the liquid content taken from the container to be tested. First, the sample liquid for determining the initial cleanness of the liquid is taken from the container according to the following method. To a test container having a volume of a (ml), there is added ultra pure water or a liquid photoresist in an amount of a half of the volume, a/2 (ml), of the container, followed by shaking it for 15 seconds, allowing it to stand over 24 hours and then collection of a sample liquid. On the other hand, the sample liquid used for the evaluation of the cleanness after the storage of the water or the liquid photoresist is taken from the container by the following method: That is, the container used for the determination of the initial cleanness is tightly sealed with a plug, then allowed to stand for a predetermined time period and then rotated over three turns while paying an attention so as not to form any air bubble, followed by the collection of a sample liquid. In the equation (1), c represents the number of fine particles, as determined using a particle counter, which are present in the whole liquid sample and have a particle size of not less than 0.2 .mu.m. Accordingly, the initial cleanness and that determined after the storage over a predetermined period of time can be calculated on the basis of the number of fine particles thus determined. In this regard, the lower the numerical value indicating the cleanness, the higher the quality of the liquid photoresist. More specifically, if the cleanness is less than 100 particles/ml, such a liquid chemical can stably be stored without causing any quality deterioration of semiconductors and liquid crystal displays (LCD) and any reduction of the yield thereof.
As containers for storing liquid photoresists and related liquid chemicals, there have usually been used, for instance, glass containers and metal containers. However, the glass and metal containers cannot ensure a high cleanness of the contents thereof. This is because sodium ions are released from the glass container and each metal container releases ions of the corresponding metal element constituting the container such as iron ions. In this respect, Japanese Patent Application Publication No. Hei 6-99000 proposes a method for eliminating these adverse effects, which comprises using a container consisting of a pouch made from an inert and corrosion-resistant plastic film (polytetrafluoroethylene film) and an external bottle or an overpack which surrounds the pouch and discharging a liquid chemical accommodated in the pouch using a dispenser.
However, such a polytetrafluoroethylene pouch cannot ensure an acceptable level of the cleanness. This method also suffers from a problem in that the pouch is disposable, but it is difficult to dispose the same after the practical use thereof. Moreover, polytetrafluoroethylene is very expensive.